Key takeaways
- What voice quality is: The clarity and reliability of audio during customer-agent phone interactions.
- Why it matters: Directly impacts customer satisfaction, NPS scores, and average handle times.
- How it’s measured: Mean opinion score (MOS), a 1-5 scale where 3.5+ is acceptable for business communication.
- Key factors affecting it: Codec incompatibility, excessive transfers, carrier issues, bandwidth constraints, and hardware problems.
I founded McIntosh & Associates to help businesses improve their customer experience by improving the performance of their contact center. We apply a data-driven approach to identify opportunities for improving contact center performance and customer satisfaction.
One of the thorniest issues we encounter is voice quality. Voice quality refers to the clarity and reliability of audio during customer-agent phone interactions, directly impacting comprehension and customer satisfaction. Good voice quality is expected by your customers, and poor voice quality leads to lower NPS scores, reduced customer satisfaction, and increased handle times. Its absence will result in significant dissatisfaction and negatively affect your NPS results.
But consistently delivering on good voice quality is easier said than done for two main reasons. First, delivering good voice quality depends on many factors working correctly. Some of these factors are under your control, and some are not. The second issue is that, for most organizations, it is very difficult to consistently know with any confidence how your voice quality is performing.
What drives poor voice quality?
First, let’s discuss some of the factors that affect voice quality. Any point on the chain from customer to agent can cause a drop in mean opinion scores (MOS), the measure of voice quality. Mean opinion score is a standardized measurement that rates perceived audio quality on a scale of 1 to 5, originally derived from human listener evaluations and now calculated algorithmically for VoIP systems. Anything from a caller having a hoarse throat, to bad audio equipment can degrade voice quality. Network and equipment effects are the most apparent and measurable.
Common causes of poor voice quality
- Codec incompatibility: Software that compresses and decompresses voice signals may not work properly between systems.
- Excessive transfers: Each call transfer can result in volume loss and signal degradation.
- Carrier issues: The caller’s voice network provider quality, such as poor cell signal based on location.
- Bandwidth constraints: Insufficient bandwidth causes packet loss, leading to jitter, echoing, and low volume.
- Hardware problems: Headset or softphone incompatibilities that degrade audio quality.
How do you measure voice quality?: Mean opinion score (MOS)
MOS is the most common measure for voice quality and is historically derived from the feedback of listeners who would sit in a “quiet room” and score a telephone call quality as they perceived it. Today, MOS is derived via algorithms that accurately measure our VoIP network performance and can categorize the quality of the voice signal that callers experience when on a call.
MOS scale reference
| Score | Quality | Description |
| 5 | Excellent | Comparable to face-to-face conversation |
| 4 | Good | Clear, effective communication |
| 3.5+ | Acceptable | Minimum threshold for business communication |
| 3.0-3.5 | Marginal | Noticeable degradation, difficult communication |
| Below 3.0 | Unacceptable | Cannot support effective communication |
Expected VoIP range: 3.5-4.2. Anything in that range is considered satisfactory; anything below that range calls for action.
Why voice quality is hard to measure
Most organizations only learn of a voice quality problem when there are escalating complaints from customers or agents. However, research indicates that the vast majority of customers won’t report when they’ve had problems. Often, the customer and agent will struggle through, talk louder, or repeat themselves. Not only is this a bad experience for your customer, but it drives average handle times. And, if the voice quality is bad enough, the customer may simply hang up and call back with the hopes of getting a better line on the next call.
Even if a customer or agent reports an issue, it’s tough to replicate. You likely won’t know details about times, locations, equipment, etc. This is all critical information you need in order to troubleshoot and resolve the issues.
Case study: voice quality assessment for a US insurance provider
One of the things that McIntosh & Associates helps businesses with is voice quality issues, and I want to share with you one particular example. We were hired by a US insurance provider to measure the voice quality across internal and vendor end-points, identify the impact of transfers, and identify site-specific issues for root cause analysis of voice quality issues.
To answer these questions, we:
- Called and recorded test 800 numbers using pre-recorded industry standard scripts where the MOS equaled five.
- Created and ran test call scenarios ranging from simple to complex with multiple calls per scenario placed to each location.
- Measured voice quality for both the agent and caller.
Case study results
- Transfer impact: 6% MOS degradation per call transfer
- Vendor vs. internal sites: 15% lower MOS at vendor sites compared to internal sites
- Current state infrastructure: MOS of 2.67 (unacceptable)
- Future state infrastructure: MOS of 3.43 (marginal improvement, still below target)
And, while the future state showed a significantly higher MOS, it was still below the target range, which was largely due to the issue with transfers.
How to improve voice quality: action steps
Based on our findings, here are concrete steps contact center managers can implement:
- Review transfer policies: Minimize unnecessary transfers and train agents on appropriate transfer protocols to reduce MOS degradation.
- Audit vendor sites: Investigate and address the performance gap between internal and vendor locations.
- Implement ongoing monitoring: Use tools like Cyara Pulse to continuously measure MOS and identify issues proactively.
- Test infrastructure changes: Measure voice quality before and after system updates to verify improvements.
- Establish MOS baselines: Set target thresholds (3.5+ minimum) and create alerts for when quality drops below acceptable levels.
Contact McIntosh & Associates to learn how we can help you improve your contact center performance, and customer satisfaction.
Contact Cyara today to learn more about how Pulse can help with ongoing monitoring.
Frequently Asked Questions
MOS is a five-point scale used to measure perceived voice quality, where 1 represents inferior quality and 5 represents excellent quality comparable to a face-to-face conversation. A score of 3.5 or higher is considered satisfactory for effective communication, while anything below that range makes it difficult to understand callers or achieve call resolution.
The expected MOS range for VoIP calls is 3.5 to 4.2, and anything within that range is considered satisfactory. Scores below 3.5 indicate a degradation in voice quality that requires action.
Common causes include codec incompatibility, bandwidth constraints leading to packet loss and jitter, hardware issues like headset or softphone incompatibilities, and the caller’s network provider. Excessive call transfers can also degrade voice quality, with each transfer leg reducing MOS by an average of 6%.
Most organizations only learn of voice quality issues when customer or agent complaints escalate, but 96% of customers will not report a problem at all. This makes proactive, ongoing monitoring essential for identifying issues before they significantly impact the customer experience.
Because the vast majority of customers do not report problems, they instead struggle through calls, speak louder, or simply hang up and call back. This means organizations miss most voice quality issues and cannot gather the details needed to troubleshoot and resolve them.
Each call transfer leg can result in a measurable drop in MOS, with research showing an average degradation of 6% per transfer. Revisiting transfer policies and agent training on appropriate transfer protocols can help reduce this impact.
Ongoing automated testing tools, such as Cyara Pulse, can continuously monitor call paths and identify process, site-specific, and network issues in real time. This approach allows teams to develop remediation plans before problems affect customers.
Yes, research has shown that internal sites can have significantly higher MOS scores than vendor sites. In one case study, internal sites outperformed vendor sites by 15%, highlighting the importance of measuring voice quality across all endpoints.